Evaluation of a commercial ELISA test kit on classical swine fever antibody detection using oral fluid samples

Classical swine fever virus (CSFV) contributes to economic loss of swine production in endemic countries. Serum neutralization and enzyme-linked immunosorbent assay (ELISA) are serological tests commonly used for monitoring CSFV antibody status with serum samples. This experiment evaluated the detection of CSFV antibody in oral fluid samples in commercial ELISA test kit by in vitro study of negative oral fluid mixed with serum of known CSFV serum neutralizing (SN) titer and in vivo oral fluid samples obtained from experimental animals. Correlations of SN titer and S/P ratio of ELISA were observed with the in vitro oral fluid samples, indicating the stability of the antibody in the oral fluid and the potential of oral fluid as an alternative specimen for CSFV diagnosis. Diagnostic sensitivity of the oral fluid detection using in vitro samples was as high as 95.83% when the ELISA procedures were modified (i.e. 12 h incubation at 4°C and addition of 100 μl antibody conjugate). The in vivo experiment used oral fluid and blood samples obtained from 20 piglets (20 days old) which were divided into 3 experimental groups: challenged with ALD strain, low virulence CSFV (A) (n=8); vaccinated (B) (n=8); and negative control (C) (n=4). The animals were vaccinated with CSFV LOM strain modified live vaccine at 0 day post inoculation (dpi) and re-challenged (A&B) with high virulence CSFV on 14 dpi and later euthanized at 30 dpi. Results from the in vivo oral fluid samples demonstrated low detectable antibody titers (SN titer 0-4) using neutralizing peroxidase-linked assay (NPLA) and all samples were negative to CSFV indirect ELISA performed at the optimal condition obtained from the in vitro protocol.

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